Lots of people have a little booze before bed to help them get to sleep — but while a night cap may help in the dozing-off department, too much alcohol can actually do a number on the overall quality of your shuteye. Let's take a look at some of the important differences between drunk sleep and sober sleep, including why it's so damn hard to sleep in after a tipple-tastic night on the town.

Dosage

Most people assume correctly that liquor and beer can actually get your eyelids feeling downright leaden, as anyone who's had a taste of alcohol has surely experienced its sleep-promoting qualities. The ethanol in your intoxicant of choice acts as a sedative, and for most people one drink is enough to feel its effects. There's even evidence that capping your intake at one brew, cocktail, or glass of grapes — what most researchers deem a "low dose" of alcohol — can actually up your total sleep time, while decreasing the number of instances you wake during the night.

Speaking of which, it's important to remember the "one drink" limit is really just a rule of thumb. Drink-ceilings vary from person to person. Plus, a single drink can have different effects even on the same individual — depending, for example, on what he or she's eaten that day. For a better idea of what your one-drink limit is, try out these handy calculators, courtesy of the NIH.

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Anyway, if you plan on downing more than one drink, you're looking at some pretty serious bedtime disturbance. In fact, even a single-cocktail nightcap can have an undesired effect on your sleep cycle if you make a habit of it. According to Timothy Roehrs and Thomas Roth — director of research and division head, respectively, of the Sleep Disorders and Research Center in Detroit, MI — the scientific literature shows that among nonalcoholics, the occasional use of alcohol as a sleep aid can improve sleep initially, but that people tend to develop a tolerance for its effects pretty quickly. As tolerance increases, so does your alcohol-intake, and then you're looking at more serious problems than an inability to get to catch some truly restful winks. Like, you know, a raging case of alcoholism.

The Rebound Effect

But even moderate alcohol consumption can ruin a good night's sleep. According to Roehrs and Roth, a modest dose of alcohol (defined as inducing a Blood Alcohol Content in the range of 0.06–0.08) within an hour of bedtime may knock you right out — but it'll exact a serious toll on your body during the second half of your normal sleep period, during what's called a "rebound effect" (emphasis added):

The term "rebound effect" means that certain physiological variables (e.g., sleep variables, such as the amount of REM sleep) change in the opposite direction to the changes induced by alcohol and even exceed normal levels once alcohol is eliminated from the body. This effect results from the body's adjustment to the presence of alcohol during the first half of the sleep period in an effort to maintain a normal sleep pattern. Once alcohol is eliminated from the body, however, these adjustments result in sleep disruption.

Given that the average person metabolizes alcohol at a rate of around 0.01% to 0.02% per hour, a person with a BAC in the range of 0.06—0.08 immediately before dozing off will finish processing the sauce in his or her system after about four or five hours. Ever woken up bright and early after a rowdy bout of late-night/early-morning boozing? Now you know why: the clearance of alcohol from your body probably triggered a rebound effect, ripping you right out of the deepest period of your sleep cycle.

"Your deep sleep is when body restores itself, and alcohol can interfere with this," says John Shneerson, head of Papworth Hospital's Resipiratory Support & Sleep Center, the largest sleep facility in the UK.

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"As the alcohol starts to wear off, your body can come out of deep sleep and back into REM sleep, which is much easier to wake from. That's why you often wake up after just a few hours sleep when you've been drinking."

So how best to ensure a restful night's sleep? Try to time it so that most of the alcohol in your system has been metabolized before you hit the hay. If you're on the cusp of being good to drive (i.e. right around a BAC of 0.08 — true for all 50 states and D.C. as of January, 2013), you'll want to quit hitting the sauce no less than four hours before bedtime. Easier in theory than in practice, we know, but at least now you know the rules your body is playing by.